Why did EPA regulate milk in the first place?

All kinds of oils, including animal fats and vegetable oils, have been considered oils under the Spill Prevention, Control, and Countermeasure (SPCC) rule based on the legislative definition of "oil" in the Clean Water Act.   Milk is considered an oil and its storage and handling have been subject to the SPCC rule, which is intended to prevent damage to the inland waters and shorelines of the United States.